Re: [julia-users] if .. else on a whole array

[Michael Borregaard]

Note that both of these versions will return an array, allowing for type 
stability

Den torsdag den 11. februar 2016 kl. 09.40.27 UTC+1 skrev Michael 
Borregaard:
>
> If you are worried about maintaining two versions, that can be solved 
> simply:
> function foo(x::Vector{bar})
>   #the main code of your function
> end
>
> function foo(x::bar)
>   foo([x])
> end
>
>
>
>

Re: [julia-users] if .. else on a whole array

[Michael Borregaard]

If you are worried about maintaining two versions, that can be solved 
simply:
function foo(x::Vector{bar})
  #the main code of your function
end

function foo(x::bar)
  foo([x])
end




Den onsdag den 10. februar 2016 kl. 13.15.30 UTC+1 skrev Ferran Mazzanti:
>
> Thanks Mauro...
>
> using two methods was the first thing I thought, but I strongly dislike 
> the idea because I'd have to maintain two different functions
> to do the same, which doubles the possibility of introducing bugs. I like 
> the idea of keeping the main function simple and unique,
> so if I change something the changes apply to all calculations in the same 
> way.
>
> Best regards,
>
> Ferran.
>
> On Wednesday, February 10, 2016 at 12:11:00 PM UTC+1, Mauro wrote:
>>
>> Probably cleanest would be to make two methods, one for scalars, one for 
>> arrays.  For the array one just loop. 
>>
>> This also works, but returns an array for scalar input (type inference 
>> should work once wrapped in a function): 
>>
>> julia> x = 5 
>> 5 
>>
>> julia> [ xi>5 ? 0:1 for xi in x] 
>> 1-element Array{Any,1}: 
>>  1 
>>
>> julia> x = 1:10 
>> 1:10 
>>
>> julia> [ xi>5 ? 0:blah for xi in x] 
>> 10-element Array{Any,1}: 
>>  1 
>>  1 
>>  1 
>>  1 
>>  1 
>>  0 
>>  0 
>>  0 
>>  0 
>>  0 
>>
>>
>> On Wed, 2016-02-10 at 11:58, Ferran Mazzanti  
>> wrote: 
>> > Hi folks, 
>> > 
>> > probably a stupid question but can't find the answer, so please help if 
>> you 
>> > can :) 
>> > I would like to evaluate a if.. else.. statement on a whole array. 
>> Actually 
>> > it's a bit more complicated, as I have a function that 
>> > previously was 
>> > 
>> > function u2(x) 
>> > return 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2) 
>> > end; 
>> > 
>> > for some other defined function u2(x) and constant L_box. The thing is 
>> that 
>> > I could directly evaluate that on a scalar x and on an array. 
>> > Now I have to change it and check if x is smaller than Lbox/2, 
>> returning 
>> > the same as above if it is, or 0 otherwise. 
>> > I tried something of the form 
>> > 
>> > function u2(x) 
>> > return x.>Lbox/2 ? 0 : 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2) 
>> > end; 
>> > 
>> > but that complains when x is an array. What would be the easiest way to 
>> > achieve this? It should work for both scalars and arrays... 
>> > 
>> > Best regards and thanks, 
>> > 
>> > Ferran. 
>>
>

Re: [julia-users] if .. else on a whole array

[Tim Holy]

If the input is a scalar and the output is a scalar, that's also type-stable. 
Type-stability is about "predictability of the output type, given the input 
types," not "always returns the same type."

Also, wrapping scalars in an array will have a significant performance cost.

Best,
--Tim

On Thursday, February 11, 2016 12:44:19 AM Michael Borregaard wrote:
> Note that both of these versions will return an array, allowing for type
> stability
> 
> Den torsdag den 11. februar 2016 kl. 09.40.27 UTC+1 skrev Michael
> 
> Borregaard:
> > If you are worried about maintaining two versions, that can be solved
> > simply:
> > function foo(x::Vector{bar})
> > 
> >   #the main code of your function
> > 
> > end
> > 
> > function foo(x::bar)
> > 
> >   foo([x])
> > 
> > end

Re: [julia-users] if .. else on a whole array

[Michael Borregaard]

Really sorry, just saw this is identical to Mauro's suggestion :-/

Michael

Den torsdag den 11. februar 2016 kl. 11.39.12 UTC+1 skrev Michael 
Borregaard:
>
> Thanks for clarifying that!
> So do you suggest
> [code]
> function foo(x::bar)
>   #the function body
> end
>
> function foo(x::AbstractVector{bar})
>   map(foo, x)
> end
> [/code]
>
> On Thu, Feb 11, 2016 at 10:33 AM, Tim Holy  wrote:
>
>> If the input is a scalar and the output is a scalar, that's also 
>> type-stable.
>> Type-stability is about "predictability of the output type, given the 
>> input
>> types," not "always returns the same type."
>>
>> Also, wrapping scalars in an array will have a significant performance 
>> cost.
>>
>> Best,
>> --Tim
>>
>> On Thursday, February 11, 2016 12:44:19 AM Michael Borregaard wrote:
>> > Note that both of these versions will return an array, allowing for type
>> > stability
>> >
>> > Den torsdag den 11. februar 2016 kl. 09.40.27 UTC+1 skrev Michael
>> >
>> > Borregaard:
>> > > If you are worried about maintaining two versions, that can be solved
>> > > simply:
>> > > function foo(x::Vector{bar})
>> > >
>> > >   #the main code of your function
>> > >
>> > > end
>> > >
>> > > function foo(x::bar)
>> > >
>> > >   foo([x])
>> > >
>> > > end
>>
>>
>

Re: [julia-users] if .. else on a whole array

[Andrew]

You can try the @vectorize_1arg macro. Just define u2 as you did, then
@vectorize_1arg Number u2.

Or, if you don't want to use the macro, you can try a for loop.  Example:

function u2(x::AbstractArray)
  out = similar(x)
  for i in eachindex(x)
out[i] = u2(x[i])
  end
  return out
end


On Wednesday, February 10, 2016 at 7:15:30 AM UTC-5, Ferran Mazzanti wrote:
>
> Thanks Mauro...
>
> using two methods was the first thing I thought, but I strongly dislike 
> the idea because I'd have to maintain two different functions
> to do the same, which doubles the possibility of introducing bugs. I like 
> the idea of keeping the main function simple and unique,
> so if I change something the changes apply to all calculations in the same 
> way.
>
> Best regards,
>
> Ferran.
>
> On Wednesday, February 10, 2016 at 12:11:00 PM UTC+1, Mauro wrote:
>>
>> Probably cleanest would be to make two methods, one for scalars, one for 
>> arrays.  For the array one just loop. 
>>
>> This also works, but returns an array for scalar input (type inference 
>> should work once wrapped in a function): 
>>
>> julia> x = 5 
>> 5 
>>
>> julia> [ xi>5 ? 0:1 for xi in x] 
>> 1-element Array{Any,1}: 
>>  1 
>>
>> julia> x = 1:10 
>> 1:10 
>>
>> julia> [ xi>5 ? 0:blah for xi in x] 
>> 10-element Array{Any,1}: 
>>  1 
>>  1 
>>  1 
>>  1 
>>  1 
>>  0 
>>  0 
>>  0 
>>  0 
>>  0 
>>
>>
>> On Wed, 2016-02-10 at 11:58, Ferran Mazzanti  
>> wrote: 
>> > Hi folks, 
>> > 
>> > probably a stupid question but can't find the answer, so please help if 
>> you 
>> > can :) 
>> > I would like to evaluate a if.. else.. statement on a whole array. 
>> Actually 
>> > it's a bit more complicated, as I have a function that 
>> > previously was 
>> > 
>> > function u2(x) 
>> > return 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2) 
>> > end; 
>> > 
>> > for some other defined function u2(x) and constant L_box. The thing is 
>> that 
>> > I could directly evaluate that on a scalar x and on an array. 
>> > Now I have to change it and check if x is smaller than Lbox/2, 
>> returning 
>> > the same as above if it is, or 0 otherwise. 
>> > I tried something of the form 
>> > 
>> > function u2(x) 
>> > return x.>Lbox/2 ? 0 : 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2) 
>> > end; 
>> > 
>> > but that complains when x is an array. What would be the easiest way to 
>> > achieve this? It should work for both scalars and arrays... 
>> > 
>> > Best regards and thanks, 
>> > 
>> > Ferran. 
>>
>

Re: [julia-users] if .. else on a whole array

[Michael Krabbe Borregaard]

Thanks for clarifying that!
So do you suggest
[code]
function foo(x::bar)
  #the function body
end

function foo(x::AbstractVector{bar})
  map(foo, x)
end
[/code]

On Thu, Feb 11, 2016 at 10:33 AM, Tim Holy  wrote:

> If the input is a scalar and the output is a scalar, that's also
> type-stable.
> Type-stability is about "predictability of the output type, given the input
> types," not "always returns the same type."
>
> Also, wrapping scalars in an array will have a significant performance
> cost.
>
> Best,
> --Tim
>
> On Thursday, February 11, 2016 12:44:19 AM Michael Borregaard wrote:
> > Note that both of these versions will return an array, allowing for type
> > stability
> >
> > Den torsdag den 11. februar 2016 kl. 09.40.27 UTC+1 skrev Michael
> >
> > Borregaard:
> > > If you are worried about maintaining two versions, that can be solved
> > > simply:
> > > function foo(x::Vector{bar})
> > >
> > >   #the main code of your function
> > >
> > > end
> > >
> > > function foo(x::bar)
> > >
> > >   foo([x])
> > >
> > > end
>
>

Re: [julia-users] if .. else on a whole array

[Mauro]

Probably cleanest would be to make two methods, one for scalars, one for
arrays.  For the array one just loop.

This also works, but returns an array for scalar input (type inference
should work once wrapped in a function):

julia> x = 5
5

julia> [ xi>5 ? 0:1 for xi in x]
1-element Array{Any,1}:
 1

julia> x = 1:10
1:10

julia> [ xi>5 ? 0:blah for xi in x]
10-element Array{Any,1}:
 1
 1
 1
 1
 1
 0
 0
 0
 0
 0


On Wed, 2016-02-10 at 11:58, Ferran Mazzanti  wrote:
> Hi folks,
>
> probably a stupid question but can't find the answer, so please help if you
> can :)
> I would like to evaluate a if.. else.. statement on a whole array. Actually
> it's a bit more complicated, as I have a function that
> previously was
>
> function u2(x)
> return 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2)
> end;
>
> for some other defined function u2(x) and constant L_box. The thing is that
> I could directly evaluate that on a scalar x and on an array.
> Now I have to change it and check if x is smaller than Lbox/2, returning
> the same as above if it is, or 0 otherwise.
> I tried something of the form
>
> function u2(x)
> return x.>Lbox/2 ? 0 : 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2)
> end;
>
> but that complains when x is an array. What would be the easiest way to
> achieve this? It should work for both scalars and arrays...
>
> Best regards and thanks,
>
> Ferran.

Re: [julia-users] if .. else on a whole array

[Ferran Mazzanti]

Thanks Mauro...

using two methods was the first thing I thought, but I strongly dislike the 
idea because I'd have to maintain two different functions
to do the same, which doubles the possibility of introducing bugs. I like 
the idea of keeping the main function simple and unique,
so if I change something the changes apply to all calculations in the same 
way.

Best regards,

Ferran.

On Wednesday, February 10, 2016 at 12:11:00 PM UTC+1, Mauro wrote:
>
> Probably cleanest would be to make two methods, one for scalars, one for 
> arrays.  For the array one just loop. 
>
> This also works, but returns an array for scalar input (type inference 
> should work once wrapped in a function): 
>
> julia> x = 5 
> 5 
>
> julia> [ xi>5 ? 0:1 for xi in x] 
> 1-element Array{Any,1}: 
>  1 
>
> julia> x = 1:10 
> 1:10 
>
> julia> [ xi>5 ? 0:blah for xi in x] 
> 10-element Array{Any,1}: 
>  1 
>  1 
>  1 
>  1 
>  1 
>  0 
>  0 
>  0 
>  0 
>  0 
>
>
> On Wed, 2016-02-10 at 11:58, Ferran Mazzanti  > wrote: 
> > Hi folks, 
> > 
> > probably a stupid question but can't find the answer, so please help if 
> you 
> > can :) 
> > I would like to evaluate a if.. else.. statement on a whole array. 
> Actually 
> > it's a bit more complicated, as I have a function that 
> > previously was 
> > 
> > function u2(x) 
> > return 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2) 
> > end; 
> > 
> > for some other defined function u2(x) and constant L_box. The thing is 
> that 
> > I could directly evaluate that on a scalar x and on an array. 
> > Now I have to change it and check if x is smaller than Lbox/2, returning 
> > the same as above if it is, or 0 otherwise. 
> > I tried something of the form 
> > 
> > function u2(x) 
> > return x.>Lbox/2 ? 0 : 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2) 
> > end; 
> > 
> > but that complains when x is an array. What would be the easiest way to 
> > achieve this? It should work for both scalars and arrays... 
> > 
> > Best regards and thanks, 
> > 
> > Ferran. 
>

Re: [julia-users] if .. else on a whole array

[Tim Holy]

I'm not quite sure if this is what you're asking, but if you want a scalar 
function to work elementwise on an array, try `map`.

--Tim

On Wednesday, February 10, 2016 04:15:30 AM Ferran Mazzanti wrote:
> Thanks Mauro...
> 
> using two methods was the first thing I thought, but I strongly dislike the
> idea because I'd have to maintain two different functions
> to do the same, which doubles the possibility of introducing bugs. I like
> the idea of keeping the main function simple and unique,
> so if I change something the changes apply to all calculations in the same
> way.
> 
> Best regards,
> 
> Ferran.
> 
> On Wednesday, February 10, 2016 at 12:11:00 PM UTC+1, Mauro wrote:
> > Probably cleanest would be to make two methods, one for scalars, one for
> > arrays.  For the array one just loop.
> > 
> > This also works, but returns an array for scalar input (type inference
> > should work once wrapped in a function):
> > 
> > julia> x = 5
> > 5
> > 
> > julia> [ xi>5 ? 0:1 for xi in x]
> > 
> > 1-element Array{Any,1}:
> >  1
> > 
> > julia> x = 1:10
> > 1:10
> > 
> > julia> [ xi>5 ? 0:blah for xi in x]
> > 
> > 10-element Array{Any,1}:
> >  1
> >  1
> >  1
> >  1
> >  1
> >  0
> >  0
> >  0
> >  0
> >  0
> > 
> > On Wed, 2016-02-10 at 11:58, Ferran Mazzanti  > 
> > > wrote:
> > > Hi folks,
> > > 
> > > probably a stupid question but can't find the answer, so please help if
> > 
> > you
> > 
> > > can :)
> > > I would like to evaluate a if.. else.. statement on a whole array.
> > 
> > Actually
> > 
> > > it's a bit more complicated, as I have a function that
> > > previously was
> > > 
> > > function u2(x)
> > > 
> > > return 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2)
> > > 
> > > end;
> > > 
> > > for some other defined function u2(x) and constant L_box. The thing is
> > 
> > that
> > 
> > > I could directly evaluate that on a scalar x and on an array.
> > > Now I have to change it and check if x is smaller than Lbox/2, returning
> > > the same as above if it is, or 0 otherwise.
> > > I tried something of the form
> > > 
> > > function u2(x)
> > > 
> > > return x.>Lbox/2 ? 0 : 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2)
> > > 
> > > end;
> > > 
> > > but that complains when x is an array. What would be the easiest way to
> > > achieve this? It should work for both scalars and arrays...
> > > 
> > > Best regards and thanks,
> > > 
> > > Ferran.

Re: [julia-users] if .. else on a whole array

[Mauro]

So, using Tim's suggestion this would be:

# assume anything which isn't an array is scalar
u2(x, Lbox) = x>Lbox/2 ? 0 : 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2)

u2(x::AbstractArray, Lbox) = map( x->u2(x,Lbox), x)

So, no code duplication.  However, on the current release writing the
second function with a loop will be more preformant (and no code
duplication either).

On Wed, 2016-02-10 at 13:21, Tim Holy  wrote:
> I'm not quite sure if this is what you're asking, but if you want a scalar
> function to work elementwise on an array, try `map`.
>
> --Tim
>
> On Wednesday, February 10, 2016 04:15:30 AM Ferran Mazzanti wrote:
>> Thanks Mauro...
>>
>> using two methods was the first thing I thought, but I strongly dislike the
>> idea because I'd have to maintain two different functions
>> to do the same, which doubles the possibility of introducing bugs. I like
>> the idea of keeping the main function simple and unique,
>> so if I change something the changes apply to all calculations in the same
>> way.
>>
>> Best regards,
>>
>> Ferran.
>>
>> On Wednesday, February 10, 2016 at 12:11:00 PM UTC+1, Mauro wrote:
>> > Probably cleanest would be to make two methods, one for scalars, one for
>> > arrays.  For the array one just loop.
>> >
>> > This also works, but returns an array for scalar input (type inference
>> > should work once wrapped in a function):
>> >
>> > julia> x = 5
>> > 5
>> >
>> > julia> [ xi>5 ? 0:1 for xi in x]
>> >
>> > 1-element Array{Any,1}:
>> >  1
>> >
>> > julia> x = 1:10
>> > 1:10
>> >
>> > julia> [ xi>5 ? 0:blah for xi in x]
>> >
>> > 10-element Array{Any,1}:
>> >  1
>> >  1
>> >  1
>> >  1
>> >  1
>> >  0
>> >  0
>> >  0
>> >  0
>> >  0
>> >
>> > On Wed, 2016-02-10 at 11:58, Ferran Mazzanti > >
>> > > wrote:
>> > > Hi folks,
>> > >
>> > > probably a stupid question but can't find the answer, so please help if
>> >
>> > you
>> >
>> > > can :)
>> > > I would like to evaluate a if.. else.. statement on a whole array.
>> >
>> > Actually
>> >
>> > > it's a bit more complicated, as I have a function that
>> > > previously was
>> > >
>> > > function u2(x)
>> > >
>> > > return 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2)
>> > >
>> > > end;
>> > >
>> > > for some other defined function u2(x) and constant L_box. The thing is
>> >
>> > that
>> >
>> > > I could directly evaluate that on a scalar x and on an array.
>> > > Now I have to change it and check if x is smaller than Lbox/2, returning
>> > > the same as above if it is, or 0 otherwise.
>> > > I tried something of the form
>> > >
>> > > function u2(x)
>> > >
>> > > return x.>Lbox/2 ? 0 : 0.5*(u2_0(x)+u2_0(Lbox-x))-u2_0(Lbox/2)
>> > >
>> > > end;
>> > >
>> > > but that complains when x is an array. What would be the easiest way to
>> > > achieve this? It should work for both scalars and arrays...
>> > >
>> > > Best regards and thanks,
>> > >
>> > > Ferran.